Wireless local area networks (WLANs) are an alternative to or an extension of wired local area networks (LANs). An access point (AP) is a hardware device that acts as a communication hub for users of a wireless device to connect to a LAN. Access points are important for extending the physical range of services in which a wireless user has access to the LAN. Access points also affect the throughput of the networks.
Access points may operate with a subscriber based smart antenna. The smart antenna is also referred to as a switched beam antenna, and generates a plurality of antenna beams. The antenna beams generated by the smart antenna include directional antenna beams and an omni-directional antenna beam.
Wireless users are also known as client stations. Example client stations are personal computers operating with a wireless network card. The wireless network card may be compatible with the 802.11 standard, for example. An access point includes an antenna for sending forward link radio frequency signals to the client stations. The access point is also responsible for receiving reverse link radio frequency signals transmitted from each client station.
In one example, a client station is wirelessly connected to an access point within the user's house. The access point has already selected a preferred antenna beam for communicating with the client station. Because of the wireless connection, the user has the option to move from room to room within the house and still be connected to the access point. When this happens, the access point typically needs to scan the antenna beams in case a better antenna beam can be selected for communicating with the client station.
One approach to address this problem is to have two phases, a scan phase and a steady transmission phase. During the scan phase, the access point sends a “dummy” frame on each directional beam to the client station, collects received signal strength indicator (RSSI) measurements on the 802.11 ACK sent by client station, and selects the directional beam with the best RSSI.
During the steady transmission phase, the access point sends a data packet on the selected best beam, measures the ACK received on the direction beam, and measures on the uplink packets received on the omni-directional antenna beam. If the RSSI measured on the omni-directional antenna beam is better than the selected directional beam, then a scan is triggered. Alternatively, if the RSSI measured on the directional antenna beam drops, then a scan is also triggered. To check for RSSI variations, a long-term and a short-term average of RSSI values are computed.
User mobility is thus currently tracked using RSSI measurements, as well as determining when to select a new antenna beam. Computing long-term and short-term averages of the RSSI values by the access point allows determination of when the client station starts to move. It is difficult to track the client station's mobility based on an average measurement. It is also difficult to differentiate changes in the environment versus changes in the client station's position. Consequently, instead of using RSSI variations to determine when to trigger a scan due to movement of the client station, other approaches are desired.